U.S. patent application number 12/727709 was filed with the patent office on 2011-09-22 for keyless/grooveless foil bearing with fold over tab.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS, INC.. Invention is credited to Steven L. Clark, Brian S. Flora, Stephan M. Ruchnewitz, Jon R. Sienkowski.
Application Number | 20110229065 12/727709 |
Document ID | / |
Family ID | 44600919 |
Filed Date | 2011-09-22 |
United States Patent
Application |
20110229065 |
Kind Code |
A1 |
Flora; Brian S. ; et
al. |
September 22, 2011 |
KEYLESS/GROOVELESS FOIL BEARING WITH FOLD OVER TAB
Abstract
An improved air foil bearing assembly is disclosed. The air foil
bearing assembly includes a bearing housing having an axially
extending bore therein and a shaft arranged within the bore for
relative coaxial rotation with respect to the bearing housing. The
shaft cooperates with the bearing housing to define an annular gap
therebetween. A foil assembly is disposed in the annular gap,
including at least one foil having at least one laterally extending
tab. The tab is adapted to be received in and extend axially from
the annular gap and is further adapted to be bent into frictional
contact with an outer surface of the bearing housing to militate
against axial movement of the foil.
Inventors: |
Flora; Brian S.; (Commerce
Twp., MI) ; Clark; Steven L.; (Farmersville, IL)
; Sienkowski; Jon R.; (Rochester, NY) ;
Ruchnewitz; Stephan M.; (Darmstadt, DE) |
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS,
INC.
Detroit
MI
|
Family ID: |
44600919 |
Appl. No.: |
12/727709 |
Filed: |
March 19, 2010 |
Current U.S.
Class: |
384/106 |
Current CPC
Class: |
F16C 32/0603 20130101;
F16C 43/02 20130101; F16C 17/024 20130101 |
Class at
Publication: |
384/106 |
International
Class: |
F16C 32/06 20060101
F16C032/06 |
Claims
1. A foil bearing assembly, comprising: a bearing housing having an
axially extending bore formed therein; a shaft arranged within the
bore for relative coaxial rotation with respect to the bearing
housing, the shaft cooperating with the bearing housing to define
an annular gap therebetween; and a foil assembly disposed in the
annular gap, the foil assembly further comprising an inner foil
portion and a bump foil portion, at least one of the inner foil
portion and a bump foil portion, at least one of the inner foil
portion and the bump foil portion having at least one laterally
extending tab, the at least one tab extending axially from the
annular gap and bent into frictional contact with an outer end
surface of the bearing housing to militate against axial movement
of the foil assembly.
2. The foil bearing assembly of claim 1, wherein the at least one
tab are secured by one of welding and bonding to the bearing
housing.
3. The foil bearing assembly of claim 1, wherein the bore of the
bearing housing is defined by an inner circumferential surface of
the bearing housing, the inner circumferential surface including an
axially extending slot, a first end of the foil assembly secured
within the slot to militate against rotational movement of the
foil.
4. The foil bearing assembly of claim 3, wherein the inner foil
portion and the bump foil portion are separate pieces.
5. The foil bearing assembly of claim 4, wherein the at least one
tab is formed adjacent a first end of the inner foil portion, and a
second tab is formed adjacent a first end of the bump portion.
6. The foil bearing assembly of claim 5, wherein a second end of
the inner foil portion extends within the annular gap in a first
direction in facing relationship to the outer circumferential
surface of the shaft.
7. The foil bearing assembly of claim 6, wherein a second end of
the bump foil portion extends within the annular gap in a second
direction in facing relationship to the inner circumferential
surface of the bearing housing.
8. The foil bearing assembly of claim 1, wherein the foil assembly
is a one-piece foil, wherein the inner foil portion extends
circumferentially in a first direction within the gap about the
shaft and the bump foil portion extends circumferentially in a
second direction within the gap about the shaft.
9. The foil bearing assembly of claim 8, wherein the bump foil
portion is disposed between the inner foil portion and an inner
circumferential surface of the bearing housing.
10. A foil bearing assembly, comprising: a bearing housing having
an axially extending bore formed therein; a shaft arranged within
the bore for relative coaxial rotation with respect to the bearing
housing, the shaft cooperating with the bearing housing to define
an annular gap therebetween; and a foil assembly disposed in the
annular gap, the foil assembly further comprising: an inner foil
portion having a first end secured to the bearing housing and a
second end circumferentially extending in a first direction within
the gap about the shaft; and a bump foil portion having a first end
secured to the bearing housing and a second end circumferentially
extending in a second direction within the gap about the shaft.
11. The foil bearing assembly of claim 10, wherein the inner foil
portion and the bump foil portion are separate pieces.
12. The foil bearing assembly of claim 11, wherein the bore of the
bearing housing is defined by an inner circumferential surface of
the bearing housing, the inner circumferential surface including an
axially extending slot, the first end of the inner foil portion and
the first end of the bump foil portion secured within the slot to
militate against rotational movement of the foil.
13. The foil bearing assembly of claim 12, wherein the first end of
the inner foil portion and the first end of the bump foil portion
each include at least one axially extending tab, the tab adapted to
be received in and extend axially from the slot and bent into
frictional contact with an outer end surface of the bearing housing
to militate against axial movement of the foil assembly.
14. The foil bearing assembly of claim 13, wherein a second end of
the bump foil portion is located between the inner foil portion and
the inner circumferential surface.
15. The foil bearing assembly of claim 10, wherein the foil
assembly is a one-piece foil, wherein the inner foil portion
extends circumferentially in a first direction within the gap about
the shaft and the bump foil portion extends circumferentially in a
second direction within the gap about the shaft.
16. A foil bearing assembly, comprising: a bearing housing having
an axially extending bore formed therein defined by an inner
circumferential surface of the bearing housing; a shaft arranged
within the bore for relative coaxial rotation with respect to the
bearing housing, the shaft cooperating with the bearing housing to
define an annular gap therebetween; a one-piece foil disposed in
the annular gap having a inner foil portion and a bump foil
portion, wherein the inner foil portion extends circumferentially
in first direction within the gap about the shaft, and the bump
foil portion extends circumferentially in a second direction within
the gap about the shaft.
17. The foil bearing assembly of claim 16, wherein the one-piece
foil is rolled within the annular gap such that the inner foil
portion is positioned radially inwardly of the bump foil
portion.
18. The foil bearing assembly of claim 16, wherein the one-piece
foil further includes at least one laterally extending tab, the tab
extending axially from the annular gap and bent into frictional
contact with an outer end surface of the bearing housing to
militate against axial movement of the foil.
19. The foil bearing assembly of claim 18, wherein the at least one
tab is located substantially adjacent the transition between the
inner foil portion and the bump foil portion.
20. The foil bearing assembly of claim 18, wherein the at least one
tab is secured by one of welding or bonding to the bearing housing
outer surface to militate against rotational movement of the foil.
Description
FIELD OF THE INVENTION
[0001] The invention relates to foil air bearings supporting a
rotating shaft of a variety of high-speed rotating systems.
BACKGROUND OF THE INVENTION
[0002] Foil air bearings are known for use with high-speed air
rotating shafts. A machine with foil air bearings is more reliable
than one with rolling element bearings because it requires fewer
parts to support the rotating assembly and needs no lubrication. In
operation, an air/gas film between a bearing and a rotating shaft
protects the foil bearing itself from wear. The bearing surface is
in contact with the shaft only when the machine starts and stops,
and a coating on the foils limits wear at those times.
[0003] The principle of an air bearing, whether of the journal or
thrust type, is simple. When two surfaces form a wedge and one
surface moves relative to the other, pressure is generated between
the surfaces due to the hydrodynamic action of the fluid carrying
the load. In a journal bearing, the shaft deflects and a wedge is
formed due to the eccentricity between the shaft center and the
bearing center.
[0004] Even though the principle of an air bearing is simple,
application is complex. For instance, in a normal journal bearing
assembly, the running radial clearance between the shaft and
bearing is extremely small (typically less than 0.0005 inch for a
2-inch-diameter shaft at 36,000 rpm, for example). Any eccentricity
in the shaft, or friction within the bearings, may cause shaft
deflection and/or shaft thermal expansion that could exceed the
running clearance, thereby reducing the useful life of the bearing
assembly. In addition, damping is required to suppress any whirl
instability, and there can be misalignment between various rotating
and stationary parts within the assembly.
[0005] Foil bearings address these problems. While the shaft is
stationary, there is a small amount of preload between the shaft
and the foil bearing. As the shaft turns, hydrodynamic pressure is
generated between the shaft and the bearing foils, pushing the
foils away from the shaft and making the shaft completely airborne.
This phenomenon occurs nearly instantly during start-up, and at a
very low speed. When the shaft is airborne, the friction loss due
to shaft rotation is extremely small. As the shaft expands or
deflects, the foils get pushed farther away, keeping an air film
clearance relatively constant. In addition, the foils provide
coulomb damping due to frictional contact therebetween, which
enhances the rotational stability.
[0006] An exemplary air foil bearing assembly 20 is shown partially
exploded in FIG. 1. The bearing assembly 20 contains a thin layer
of top foil 22 supported on a corrugated or "bump" foil 24. The
bump foil 24 is arranged on the inner circumferential surface 26 of
the bearing housing 28, and the top foils 22 is inserted on the
inner annular surface 30 of the bump foil 24. At least an inner
annular surface 32 of the top foil 22 is typically coated with a
solid film lubricant to provide low contact friction between a
rotating shaft (not shown) and the inner annular surface 32 of the
top foil 22.
[0007] The bump foil inner annular surface 30 is in frictional
contact with an outer annular surface 34 of the top foil 22,
providing support to the top foil 22. The corrugations 36 of the
bump foil 24, as well as the thickness of the bump foil 24, are
designed to provide a desired stiffness, and spring force between
the bearing housing inner circumferential surface 26 and the top
foil 22 to provide the desired bearing load support capacity.
Typically, a small amount of preload is desired between the shaft
(not shown) and the inner annular surface 32 of the top foil 22
when the shaft is at rest. During shaft rotation, air is drawn
between the shaft and the top foil inner annular surface 32, where
it is compressed. Due to hydrodynamic action, the compressed air
deflects the top foil 22 away from the shaft and the shaft is
supported by a cushion of air. As the top foil 22 deflects radially
outwardly, it is supported by the corrugations 36 of the bump foil
24. Depending upon the magnitude of the hydrodynamic forces, the
corrugations 36 elastically deform, thereby providing a compliant
feature of the bearing assembly 20. In particular, the
pre-determined spring rate of the bump foil 24 accommodates shaft
expansion, shaft excursion and housing misalignment. The
corrugations 36 also provide a flow path for a small amount of
cooling air, thereby maintaining a desired temperature in the
bearing assembly 20.
[0008] Typically, both the top foil 22 and the bump foil 24 are
separately stamped from sheet metal having a desired thickness. The
bumps 36 may be formed in the bump foil 24 as part of the stamping
process, or they may be formed in a second stamping or rolling
operation. The ends 40 of the top foil 22 are formed with a ninety
degree flange that is affixed to a metallic key 42, usually by a
spot welding or other bonding operation. Similarly, the ends 44 of
the bump foil 24 are each formed with a ninety degree flange, and
are affixed to the metallic key 42 by a spot welding or other
bonding operation, wherein the bump foil is located between the top
foil 22 and the inner circumferential surface 26 of the bearing
housing 28 when assembled into the housing 28 (FIG. 2). The key 42,
including the ends 40, 44 respectively of the top foil 22 and the
bump foil 24, is then inserted into a machined keyway 46 formed in
the bearing housing 28. Insertion of the key 42 into the keyway 46
prevents rotational movement of the top foil 22 and the bump foil
24, which is crucial to proper air bearing operation. To prevent
axial migration of the foils 22, 24 within the bearing housing,
plates 48 are then attached to the outer surface 38 of the bearing
housing 28, typically by spot welding or other bonding operation,
wherein the plates 48 cover the ends of the keyway 46. Machining
the keyway, welding each of the ends 40, 44 respectively of the top
foil 22 and the bump foil 24 to the key 42, and welding the plates
48 to the outer surface 38 of the bearing housing 28 are complex,
time-consuming manufacturing operations. It would be desirable to
develop an air foil bearing requiring less complex manufacture
while retaining the desirable bearing and functional
characteristics.
SUMMARY OF THE INVENTION
[0009] Concordant and consistent with the present invention, an
improved air foil bearing assembly is disclosed, comprising a
bearing housing having an axially extending bore therein; a shaft
arranged within the bore for relative coaxial rotation with respect
to the bearing housing, the shaft cooperating with the bearing
housing to define an annular gap therebetween; a foil assembly
disposed in the annular gap, the foil assembly further comprising
at least one foil having at least one laterally extending tab, the
tab adapted to be received in and extend axially from the annular
gap and adapted to be bent into frictional contact with an outer
surface of the bearing housing to militate against axial movement
of the foil.
[0010] In one embodiment, the inner circumferential surface of the
bearing housing includes an axially extending thin slot, and the
respective first ends of the top foil and the bump foil include at
least one axially extending tab, the tab adapted to be received in
and extend axially from the thin slot. The at least on tab is
further adapted to be bent into frictional contact with an outer
surface of the bearing housing to militate against rotational
movement of the top foil and the bump foil.
[0011] In another embodiment, an improved air foil bearing assembly
is disclosed, comprising a bearing housing having an axially
extending bore therein defining an inner circumferential surface; a
shaft arranged within the bore for relative coaxial rotation with
respect to the bearing housing, the shaft cooperating with the
bearing housing to define an annular gap therebetween; an elongate
foil having a first substantially flat end portion and a second
substantially corrugated end portion, the first end portion adapted
to be concentrically wound inside the second end portion within the
gap; the elongate foil including at least one axially extending tab
adapted to axially extend from the annular gap, the at least one
tab further adapted to be secured to an outer surface of the
bearing housing.
DESCRIPTION OF THE DRAWINGS
[0012] The above, as well as other advantages of the present
invention, will become readily apparent to those skilled in the art
from the following detailed description of a preferred embodiment
when considered in light of the accompanying drawings in which:
[0013] FIG. 1 is a partially exploded perspective view of an air
foil bearing assembly as known in the art;
[0014] FIG. 2 is an elevational view of the air foil bearing of
FIG. 1;
[0015] FIG. 3 is a top plan view of foil bearings according to an
embodiment of the invention;
[0016] FIG. 4 is an end elevational view of the assembled air foil
bearing assembly according to the embodiment shown in FIG. 3;
[0017] FIG. 5 is a top plan view of a foil bearing according to
another embodiment of the invention; and
[0018] FIG. 6 is a perspective view of the assembled air foil
bearing assembly according to the embodiment shown in FIG. 5.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0019] The following detailed description and appended drawings
describe and illustrate various exemplary embodiments of the
invention. The description and drawings serve to enable one skilled
in the art to make and use the invention, and are not intended to
limit the scope of the invention in any manner. In respect of the
methods disclosed, the steps presented are exemplary in nature, and
thus, the order of the steps is not necessary or critical.
[0020] FIG. 3 illustrates a top foil 122 and a corrugated or "bump"
foil 124 of an air foil bearing. As in the prior art, both the top
foil 122 and the bump foil 124 are separately stamped from sheet
metal to have a desired thickness. At least an inner surface 132 of
the top foil 122 is typically coated with a solid film lubricant to
provide low contact friction between a rotating shaft 172 shown in
FIG. 4. and the inner surface 132 of the top foil 122. The
corrugations 136 may be formed in the bump foil 124 as part of the
stamping process, or they may be formed in a second stamping or
rolling operation.
[0021] The top foil 122 includes a first end 150 and a second end
152. A pair of laterally extending tabs 154 is formed adjacent the
first end 150. The tabs 154 are formed so that when the top foil
122 is inserted into an annular gap between a bearing housing 128
and the shaft 172, the tabs 154 extend axially with respect to the
shaft 172. The tabs 154 may be integrally formed with the top foil
122, or they may be added at any time during the manufacturing
process, as desired. Additionally, the tabs 154 may have a
different thickness from the top foil 122, either to add stiffness
to the top foil 122 or to improve the bend-ability of the first end
152 of the top foil 122.
[0022] Similarly, the bump foil 124 includes a first end 160, a
second end 162, and a pair of laterally extending tabs 164 adjacent
the first end 160 of the bump foil 124. The tabs 164 are formed so
that when the bump foil 124 is inserted into an annular gap between
the bearing housing 128 and the shaft 172, the tabs 164 extend
axially with respect to the shaft 172. The tabs 164 may be
integrally formed with the bump foil 124, or they may be added at
any time during the manufacturing process, as desired.
Additionally, the tabs 164 may have a different thickness from the
bump foil 124, either to add stiffness to the bump foil 124 or to
improve the bend-ability of the first end 162 of the bump foil
124.
[0023] The top foil 122 and the bump foil 124 are inserted into a
bearing assembly 120, shown in FIG. 4. The bearing assembly 120
includes the bearing housing 128 having an axially extending bore
defined by an inner circumferential surface 126. An axially
extending slot 170 is formed into the inner circumferential surface
126. The bearing housing 128 cooperates with the shaft 172 to
define an annular gap 174 between the bearing housing 128 and an
outer circumferential surface 176 of the shaft 172. The first end
150 of the top foil 122, including the laterally extending tabs
154, is received within the slot 170, while the second end 152 of
the top foil 122 extends circumferentially in a first direction
178, wherein the top foil 122 is in facing relationship with the
bearing housing inner circumferential surface 126 and the outer
circumferential surface 176 of the shaft 172. The top foil second
end 152 may extend part, all, or more than all of the way about the
outer circumferential surface 176 of the shaft 172, as desired and
as required for proper operation of the bearing assembly 120. In
one embodiment, the laterally extending tabs 154 of the top foil
122 extend axially from the slot 170 past an outer end surface 138
of the bearing housing 128. The tabs 154 are bent into frictional
contact with the outer end surface 138 of the bearing housing 128.
If desired, the tabs 154 may optionally be secured to the outer end
surface 138 of the bearing housing 128 by welding or bonding.
Insertion of the first end 150, including the tabs 154, into the
slot 170 acts to militate against rotational movement of the top
foil 122. Additionally, optional welding or bonding of the tabs 154
to the outer end surface 138 of the bearing housing 128 militates
against axial movement of the top foil 122, maintaining the
position of the top foil 122 between the shaft 172 and the bearing
housing 128.
[0024] Similarly, the first end 160 of the bump foil 124, including
the laterally extending tabs 164, is received within the slot 170,
while the second end 162 of the bump foil 124 extends
circumferentially in a second direction 180, wherein the bump foil
124 is in facing relationship with the bearing housing inner
circumferential surface 126 and the outer circumferential surface
176 of the shaft 172. The bump foil second end 162 may extend part,
all, or more than all of the way about the housing inner
circumferential surface 126, as desired and as required for proper
operation of the bearing assembly 120. In one embodiment, the
laterally extending tabs 164 of the bump foil 124 extend axially
from the slot 170 past the outer end surface 138 of the bearing
housing 128. The tabs 164 are bent into frictional contact with the
outer end surface 138 of the bearing housing 128. If desired, the
tabs 164 optionally may be secured to the outer end surface 138 of
the bearing housing 128 by welding or bonding. Insertion of the
first end 160, including the tabs 164, into the slot 170 acts to
militate against rotational movement of the bump foil 124.
Additionally, optional welding or bonding of the tabs 164 to the
outer end surface 138 of the bearing housing 128 militates against
rotational movement of the bump foil 124, maintaining the position
of the bump foil 124 between the top foil 122 and the bearing
housing 128. Typically, the bump foil 124 is installed such that
the bump foil second end 162 is located between the top foil 122
and the bearing housing inner circumferential surface 126.
[0025] When compared to the bearing assembly 20 of FIG. 1, the
bearing assembly 120 of FIGS. 3 and 4 advantageously requires fewer
parts, fewer welds, and less time to assemble. In particular, the
bearing assembly 120 eliminates the key 42 and the end plates 48.
Additionally, less precision is required to form the thin slot 170
instead of a precisely machined keyway 46. Instead, a width w of
the slot 170 need only be slightly more than a combined thickness
of the top foil 122 and the bump foil 124, although it should be
understood that the width w of the slot 170 may be modified as
desired for a particular application.
[0026] A one-piece foil 190, shown in FIG. 5, may be used to
further minimize the assembly complexity of an air foil bearing.
The one-piece foil 190 combines features of both a top foil and a
bump foil into a single piece. In particular, the one-piece foil
190 may be formed from an elongate sheet, and may be divided along
its length L into a substantially flat inner foil portion 192 and a
bump portion 194. The relative proportions of the inner foil
portion 192 and the bump portion 194 of the one-piece foil 190 may
be modified for specific applications and annular gap sizes. As
non-limiting examples, the inner foil portion 192 may be
substantially equal in length to the bump portion 194, or the inner
foil portion 192 may be longer or shorter than the bump portion
194, as desired. Additionally, the inner foil portion 192 and the
bump portion 194 may be individually formed and interconnected in a
separate manufacturing step, or they may be integrally formed as a
single stamping or rolling operation. After the stamping or rolling
operation, an inner surface 196 of the inner foil portion 192 may
be coated with a solid film lubricant to provide low contact
friction between a rotating shaft (not shown) and the inner annular
surface 196 of the inner foil portion 192. Similarly, the
corrugations 195 of the bump portion 194 of the foil may be created
during the stamping or rolling process, or they may be formed in a
later manufacturing operation. Additionally, the bump portion 194
may be treated, such as by an annealing process after manufacture
of the one-piece foil 190, as desired.
[0027] The one-piece foil 190 further includes at least one, and
usually a pair, of laterally extending tabs 198 formed along the
length L of the one-piece foil. The location of the tabs 198 may be
anywhere along the length L, but favorable results have been found
when the tabs 198 are located adjacent a midpoint 200 of the length
L of the one-piece foil 190. The tabs 198 are formed so that when
the one-piece foil 190 is inserted into an annular gap between a
bearing housing and a shaft, the tabs 198 extend axially with
respect to the shaft. The tabs 198 may be integrally formed with
the one-piece foil 190, or they may be added at any time during the
manufacturing process, as desired. Additionally, the tabs 198 may
have a different thickness from the one-piece foil 190, either to
add stiffness to the foil 190 or to improve the assembly
process.
[0028] As shown in FIG. 6, the one-piece foil 190 may be inserted
within a bearing housing 228 to form a bearing assembly 220. The
bearing housing 228 includes an axially extending bore 268 that is
defined by an inner circumferential surface 226. However, unlike
the bearing assembly 120 of FIG. 4, the inner circumferential
surface 226 does not include a slot or a keyway.
[0029] The bearing housing 228 cooperates with a shaft (not shown)
to define an annular gap between the bearing housing 128 and an
outer circumferential surface of the shaft. The one-piece foil 190
is rolled wherein the inner foil portion 192 of the one-piece foil
190 is rolled radially inwardly of the bump portion 194. The bump
portion 194 is therefore interposed between the inner foil portion
192 and the inner circumferential surface 226 of the bearing
housing 228. Such an arrangement generally requires that the inner
foil portion 192 extend circumferentially in a first direction 278,
placing the inner foil portion 192 in facing relationship with the
shaft. The inner foil portion 192 may extend part, all, or more
than all of the way about the outer circumferential surface of the
shaft, as desired and as required for proper operation of the
bearing assembly 220. Likewise, the bump portion 194 may extend
part, all, or more than all of the way about the inner
circumferential surface 226 of the bearing housing 228, as desired
and as required for proper operation of the bearing assembly
220.
[0030] The laterally extending tabs 198 of the one-piece foil 190
extend axially past an outer end surface 238 of the bearing housing
228. The tabs 198 are bent into frictional contact with the outer
end surface 238 of the bearing housing 228. If desired, the tabs
198 may be secured to the outer end surface 238 of the bearing
housing 228 by welding or bonding, thereby militating against
rotational movement of the one-piece foil 190. Additionally,
welding or bonding the tabs 198 to the outer end surface 238 of the
bearing housing 228 militates against axial movement of the foil
190, maintaining the position of the foil 190 within the gap
between the shaft and the bearing housing 228.
[0031] A one-piece foil 190 therefore minimizes a complexity of the
bearing housing 228. When compared to the bearing assembly 20 of
FIG. 1, the bearing assembly 220 of FIG. 6 advantageously requires
fewer parts, fewer welds, and less time to assemble. In particular,
the bearing assembly 220 eliminates the key 42, the keyway 46, and
the end plates 48.
[0032] While certain representative embodiments and details have
been shown for purposes of illustrating the invention, it will be
apparent to those skilled in the art that various changes may be
made without departing from the scope of the disclosure, which is
further described in the following appended claims.
* * * * *